A high field strength which allows recording on a medium having high heat stability and a high field gradient for forming a steep boundary between bits is very beneficial to the field of data storage since it may be used to increase a recording density in perpendicular magnetic recording on magnetic media, which may be used with a hard disk drive (HDD). However, it is difficult to maintain or improve field strength while maintaining a high heat stability and a high field gradient as the size of the magnetic pole's air bearing surface, which provides for the increased track density, becomes smaller. This is because the saturation magnetic flux density of the pole which most strongly affects the recording field characteristics, and the distance between the magnetic head and the recording medium, are generally close to the physical and technical limits of conventional technologies, and scaling these dimensions down in proportion to the pole size leads to breakdown or failure. This currently is a fundamental issue in magnetic recording systems.
In addition, the abovementioned limits also affect the shape of the magnetization pattern formed on the recording medium. The shape of the recording bits generally reflects the head field distribution. That is to say, a magnetization pattern which has a scaling relationship with the pole shape is formed on the recording medium by the magnetic flux which is isotropically dissipated from the pole. This means that if the head dimensions and the distance between the magnetic head and the medium are all proportionately compressed under fixed conditions of saturation magnetic flux density, the shape of the magnetization pattern will also be proportionately compressed. However, in the present situation where the reduction in the distance between the magnetic head and the medium is insufficient, the pole shape and field distribution deviate from the scaling relationship, and the magnetization pattern is distorted, which is undesirable.
The most striking effect due to this phenomenon is the curvature of the recording transition line. As shown in FIG. 1, which is a schematic of a magnetization pattern formed on a medium according to the prior art, the problem of the curvature of the recording transition line has already been identified, and it is an issue that needs resolving in order to increase track density. Japanese Patent No. 4118246, for example, discloses technology for resolving this issue, in which the end of the pole is made to curve in the opposite direction to the magnetization pattern. Also, Japanese Unexamined Patent Appl. Pub. No. 2006-196142 proposes forming a pole from a material such that the saturation magnetic flux density decreases toward the center from the peripheral edge of the pole.
However, both of the solutions presented above according to the prior art has an intrinsic problem in that the magnetic field strength is reduced, and a reduction in the curvature of the transition line makes it difficult to obtain suitable recording characteristics, such as field gradient and saturation recording performance.
Therefore, a solution that can provide a high magnetic field strength which allows for recording on a magnetic medium having high heat stability and a high field gradient for forming a steep boundary between bits would be very beneficial to the field of data storage.